Electric arc furnaces (EAFs) make steel by using an electric arc to melt one or more charges of scrap metal, hot metal, iron based materials, or other meltable materials, which is placed within the furnace. Modern EAFs may also make steel by melting DRI (direct reduced iron) combined with the hot metal from a blast furnace. In addition to the electrical energy of the arc, chemical energy is provided by auxiliary burners using fuel and an oxidizing gas to produce combustion products with a high heat content to assist the arc.
If the EAF is used as a scrap melter, the scrap burden is charged by dumping it into the furnace through the roof opening from buckets, which also may include charged carbon and slag forming materials. A similar charging method using a ladle for the hot metal from a blast furnace may be used along with injection of the DRI to produce the burden. Additionally, these materials could be added through other openings in the furnace.
In the melting phase, the electric arc and burners melt the burden into a molten pool of metal, termed an iron carbon melt, which accumulates at the bottom or hearth of the furnace. Typically, after a flat bath has been formed by melting of all introduced burden, the electric arc furnace enters a refining and/or decarburization phase. In this phase, the metal continues to be heated by the arc until the slag forming materials combine with impurities in the iron carbon melt and rise to the surface as slag. During the heating of the iron carbon melt, it reaches the temperature and conditions when carbon in the melt combines with oxygen present in the bath to form carbon monoxide bubbles. Generally, flows of oxygen are blown into the bath with either lances or burner/lances to produce a decarburization of the bath by the oxidation of the carbon contained in the bath.
A furnace must reach very high temperatures to melt burden into molten metal. For example, scrap steel melts at approximately 2800° F. Additionally, it is typically desirable to raise the temperature of the melt sufficiently above the melting point (typically to 2950° F.-3050° F.) to allow the melt to be transferred from the furnace to a desired location and further processed without prematurely solidifying. In addition to melting the scrap, the electric arc and molten burden can damage the furnace itself as well as any devices placed inside the furnace, such as burners, lances, and enclosures for burners and lances.
To combat heat related problems, furnace and furnace component designers generally use water cooled devices and panels. Such devices and panels use a constant flow of cooling fluid through the devices, close to the surfaces that are exposed to heat, to help dissipate the heat. The cooling fluid thus cools the panels, from the inside, and lowers the temperature of the device.
Most fluid cooled devices use a serpentine arrangement to direct water through the device. While such arrangements are often effective at cooling furnace components, they are not sufficiently efficient and often allow hot spots to develop. One reason why a serpentine arrangement is not efficient is that as the water flows through the device, small bubbles often form along the walls of the water pipes. These bubbles can insulate a portion of the pipe and prevent the water from cooling the device sufficiently.
Within a cooling pipe, cooling fluid generally moves most rapidly and turbulently through the center of the pipe, and likewise it moves less rapidly and less turbulently along the walls of the pipe. Those skilled in the art may be familiar with the Reynolds number of a flow. The Reynolds number is indicative of the turbulence of the fluid. A low Reynolds number indicates that the fluid flow is laminar and a high Reynolds number indicates that the fluid flow is turbulent. In cooling operations, it is desirable for the fluid flow to be turbulent and thus a high Reynolds number is desired. Often, the turbulence of the fluid along the pipe wall is low even when the overall fluid flow through the pipe is high. One solution to solving this problem is to place material along the wall in the pipe to partially obstruct the flow and to increase the turbulence of the fluid along the pipe wall. While this solution may improve the turbulence of the fluid in a location, it may cause other areas of low turbulence to form.
Another remedy to this problem is to increase the velocity and turbulence of the water by increasing the flow of water through the pipe. This may help wash away the bubbles, but it requires significantly higher water flow and pressure, thereby increasing the cost of operations.
Further, certain portions of a furnace device may experience greater heat effects than other portions of the device. The serpentine structure does not allow a furnace device to receive more cooling in one area than another. Rather, the same force of water flows through all sections of the serpentine.
One solution used to address the problems associated with the serpentine structure is the use of spray nozzles to spray the walls of a furnace to keep them cool. One such solution is disclosed in U.S. Pat. No. 4,813,055 to Heggart et al (hereinafter “Heggart”). In Heggart, a furnace is built with an inner and an outer shell and spray nozzles are installed between the two shells to spray and cool the outside of the inner shell. While this solution often works effectively for furnace walls, it is not practical for use in furnace components due to space limitations.
Therefore, it would be advantageous to provide a method and apparatus for cooling furnace devices that overcome the problems associated with serpentine water cooling and spray system water cooling.
Additionally, it would be advantageous to provide a method and apparatus for cooling furnace devices that allows cooling fluid to be directed to specific portions of the furnace device.